This invention relates to devices for adjusting idler pulleys and more particularly to the devices for adjusting such pulleys used in the belt sanding machine.
This device is an improvement of the adjustment means disclosed in U.S. Pat. Nos. 2,706,367 and 3,909,987 and is particularly useful in machines having a sanding belt tightly wound on three co-planar pulleys. A frequent problem with sanders of these types is the slippage and loosening of the sanding belt due to misalignment of the pulleys. At times, if not corrected, the belt may even come off which could result in damage to a work piece or even injury. For this reason it is important that the belt be accurately centered on properly aligned pulleys during operation of the sander.
It was found that accurate centering of the belt was sensitive to alignment of the pulley. This knowledge resulted in the development of the invention described in U.S. Pat. No. 2,706,367. The adjustment device disclosed in that patent had provided a satisfactory solution to the adjustment problem. It was then realized that improvements in the adjusting mechanism could be made.
Part of the mechanism of U.S. Pat. No. 2,706,367 included a finger having an off-center boss engaging an arm. The adjustment was as simple as it could be, because the adjusting finger could make a complete revolution of 360 degrees. Also the snug fit of the boss and arm could easily bind by being clogged with the dust from the sander.
Since only slight adjustments of the idler puller were necessary, it was found that a flat adjustable arm using loose-fitting slots not only provided a much freer adjustment but also provided a convenient guide to limit the maximum adjustment. Also the device was easier to assemble and disassemble and has one less part. That improvement is disclosed in U.S. Pat. No. 3,909,987.
Since the previously mentioned patents, a new and third improvement means for the centering and adjusting the sanding belt has been found. The flat adjustable arm using loose fitting slots has been eliminated. Further, the square shoulder necessary with the first adjustment to maintain the orientation of the pulley shaft relative to the slot has also been eliminated. The new adjustment means rigidly secures the member with the square shoulder to a new tracking bracket placed below the hanger. The tracking bracket holds the shaft and prevents it from turning by securing it to the bracket by a screw. There are two adjustment means for this new method; one is a tracking knob having a shaft offset from the tracking bracket which in turn rotates the tracking bracket, and there is a spring towards the other end of the bracket for biasing the bracket. In-line and below the center of the tracking bracket is a set screw which adjusts the shaft and pulley and a second axis perpendicular to the first axis of adjustment.
Accordingly, it is an object of the present invention to provide an idler pulley adjustment device which has a tracking bracket biased on one end by a spring and pushed and rotatable by a tracking knob and threaded shaft.
Another object of the present invention is to provide an idler pulley adjustment mechanism having a set screw through the upright plane and providing adjustment of the lower or second adjustable member independently of the adjustment caused by the tracking knob and threaded shaft. These and other objects will become apparent when the description is considered in conjunction with the accompanying drawings.